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nveyzfar- /nesses- KM 45,0 w wg; j y '7 ll l r omas ravens co,muvo-umwwumafou n c DR. H. voert., or Banus, PRUss'iA, Assieme-'ro wnsoNAND' noon f or PHILADELPHM, PENNSYLVANIA.

Letters .Patent No. 75,493, dated llarch i0, 1868.

vIlllllltOVFlVlEN'I IN PHOTOMETERS.

ro ALLvwHoM rr MAY- eoNcERN;

Be it known that I, Dr. H. VOGEL, of Berlin", Prussia, have invented anew and improved Photometer; and- I do hereby declare that the-followingis a full,.clcar, 'and exact description thereof, which will enableothers skilled Jin the 'art-to make and use .the same, reference beinghad tothe accompanying drawings, forming part of this specification, in'which-Q- Figure l represents a perspective viewof'my improvedphotcmeter. Figure 2 is longitudinal vertical sectio'n of the same.Figure' is a vertical transverse section of the same. Similar letters ofreference indicate corresponding parts.

The object of this invention is to determine, with exaetness, -the timerequired for copying photographic. negatives. v i i i By thecopyingprocess, positives are to be produced upon papier from a negativetaken in the camera.v

For this' purpose a piece of very sensitive paper is placed upon thenegative, and into the lightnin which" it remains until it has receivedthe required impression fromv the negative. This impression isei-thervdirectly visible or. is made visible by a separate process. Ifit is directly visible, it is easy to determine the lengtlrof timeduring which the paper and negative are to bc ezgposcd'to the light, asthe progressief the copying process canbe easily noticed. But if the.process 'is invisible, it is imperatively necessary to determinebeforehand the required length of time. If the right time has not been.chosen, itis impossible to correct the mistake. -But it is verydifficult to determine the time, owing to the variations of the chemical,intensity of daylight.' 'lfo overcome"thesediiculties is the object ofmy invention', by means .of which the necessary length of time for'exposing any desired pieture in any desired weather to the light can atonce be ascertained.

in the drawing, represents a box, made of wood or other suitablematerial, of suitp'ble size and shape, and providedwith a hinged lid, B,as shown. I The lid B consists of a wooden o r other frame, a, by whicha ',iglass'plate, b, is held. On the under-side of this glass plate issecured a series'of'thin strips of paper, C, which are arranged inlayers, each lower layer projecting beyond the edge of the layer aboveasis clearly shown in iig. 2, 'The, step system thuisl producedrepresenten semi-transparent medium, the transparency of. -whichdecreases by degrees toward the thicker end. Black .figures upon theunder side of the lower longest Vstrip of paper indicatethe' number oflayers arranged above each such `gure, as will be clearly understoodfrom figs. 1 and 2. AThe whole cover B, with the paper system on it. canbe'folded down and fastened, by meansv offa small hook, c,-,or "otherequivalent device. l

Within the box A is arranged a sliding false bottom, D, which is, bymeans of a springl or springs, E, pressed upward against the paper, C,as shown'ing. 2. Upon this false bottom are placed a number ofsensitive-paper strips. -For this purpose I do not use silvered paper,which can only be preserved a short time, but paper' which has b'eensaturated with alkaline ehromate, and which, as I have found, canvbepreserved'for four weeks; These paper strips are presscdrmly against theunder side'oi` the paper, C, so as to fit well to the same. If thisapparatus is then exposed to the light, the separate sections of theupper sensitive paper will be successively darkenedfrst that portionunder No. 1, then that under No. 2, ofthe paper, C, and so forth. Thepaper will gradually become darker 'towards the thicker portion of thepaper, C; the quicker, the more sensitive the paper is. Now it will beeasy to recognize how far the chemical effect of the light has operated,:is the printed portions of the paper, C, do not let the lightpassvthro'cgh the paper, and will consequently leave that portion of thelower sensitive paper which is under thergure light, and these {ign'resvwill therefore remain light on the sensitive paper after the* same hasbeen aiected by the light. If the box is then opened in a not very lightroom, the place, to which the light'has been able to atleet thechromo-paper will lbe easily ascertained, and the last ligure thus-produced oli-the paper will showhow many thicknesses of the paper, C,the light hasbeenable to pass through, during a given space of time,whichoccupies but a few seconds'.

With this device will be easy to indicate the correct timefor exposing anegative to the light, especially when thelnovel carbonprint'isemployed; The instrument isexposed to the light atvthe same time asthenegativ'e whichis tobe copied, and if the instrument shows sixdegrees, the irst'quartr o f the negative is the required intensity. The'same' is the correct degree for copying. j

covered; if eight, the-second; if ten, the third; and if twelve, thefourth. In vthis manner the sinjgle parts to 6, 8, 10,v and 12, havebeen copied. The picture is then developed, and notice is .taken whichpart .of it shows If a number of negatives are to beprinted, they arearranged according to their intensitygivhich is easily done by experts,and are then divided into three classes, so that they can beeasilymanaged. I y

vThis apparatus ean also he used with good advantage for indicating thetime of taking negatives in lthe camera from bodies. v

Having described my invention, what I claim as new, and desire to sechreby Letters Patent, is

1. The arrangement of the transparent paper strips C, which ar'earranged in steps, and which -axe divided into sections, each sectionhaving an opaqte portion, substantially as herein shown and described.

2. The box A,when provided with a cover, B, 4having a glass' plate, b,and the step-formed paper C, and

with the sliding false bottom D pressed against `the paper C, by meansof a spring, E, as set forth, :illv niade and operating substantially asherein shown and described.

3. 'lhe paper strips, saturated with alkaline'chromate, when they areapplied lo a photometer, snbstantially as herein shown and described.

n The above speciiieatonuof my invention signed by me, thisv twentiethday :of November, 1867. l DB. 11.--VOGEL.

Witnesses:

v13. BnEKMNN, J. C. 'ScHAAnwcnrnm

